问题 问答题

在做“探究小车速度随时间变化的规律”的实验中,电磁打点计时器应该接在50Hz的(填“高压”或“低压”______ 电源上.如图8所示是某次实验中得到的一条纸带,从比较清晰的点起,每隔4个打印点取一个点作为计数点,分别标明0,1,2,3,4,则相邻两个计数点之间的时间间隔为______s.现测得图中0与1两计数点间的距离s1=30mm,3与4间距离s4=48mm,则小车的加速度为______m/s2;小车在打点计时器打“3”这一点时的瞬时速度为______m/s.

答案

电磁打点计时器是使用低压交流电源的仪器,若电源频率为50Hz,则每隔0.02s打一个点,若每隔4个打印点取一个点作为计数点,则计数点之间的时间间隔为0.1s;

根据匀变速直线运动的推论△x=aT2,有:

s4-s1=3aT2,所以:a=

s4-s1
3T2
=
(48-30)mm
3×(0.1s)2
=0.6m/s2

根据s4-s1=3aT2,连续相等时间间隔的位移差为△x=aT2=6mm,所以2、3之间距离为:s3=42mm

根据匀变速直线运动中时间中点的速度等于该过程中的平均速度,有:

v3=

s3+s4
2T
=
(32+48)mm
2×0.1s
=0.45m/s

故答案为:低压;0.1; 0.6; 0.45.

阅读理解

阅读理解。

     根据短文内容选择正确答案。

     England in summer is like a large well-kept garden. According to a recent study, about 80% of British

people dream of living in the countryside, while only about 20% of them are living there.     

     English village communities (社区) are small. They are, however, warm and usually welcoming. The

post office is usually the center of every village. It offers a chance to newcomers (新来者) to get to know

the local culture.     

     Maggie moved from the city to the countryside of England three months ago. For her, getting to know

the local people hasn't been a problem. The post office has been the main place for communicating and

neighbors often greet her in the street. She found herself quickly get used to the community and make new friends. People always invite her to children's parties.    

     Maggie's neighbors are all easy-going (随和的). Maggie says that even if the local people are interested in her background (背景), so far no one has said anything. "Unlike Chinese people, English people go

around the sun to meet the moon, "Maggie says.    

     She thinks that the village life is wonderful and she likes her present life very much.     

1. According to the study, how many English people dreaming of living in the countryside have realized their dream?

A. About 20%.

B. About 60%.

C. About 80%.

D. About 100%.

2. What does the writer think of English village communities?

A. Small and boring.

B. Small but noisy.

C. Small but comfortable.

D. Dirty and small.

3. How long has Maggie lived in the countryside?

A. For three years.

B. For three months.

C. For three weeks.

D. For three days.

4. What can we know from Maggie's words, "Unlike Chinese people, English people go around the sun to meet the moon"?

A. Chinese people are more kind-hearted than English people.

B. English people like Chinese people very much.

C. Chinese people travel to the sun through the moon.

D. English people don't show their opinions in direct (直接的) ways.

5. What's the passage mainly about?of England.

A. How to communicate with English people.

B. The comfortable life in an English village.

C. Maggie's new neighbors.

D. The culture

单项选择题